U.S. Pat. No. 4,941,822 is directed to an apparatus for heat treating contaminated particulate material, such as waste foundry sand, which contains an inorganic binder, such as clay, or organic binders.
In the apparatus of the aforementioned patent, an auger projects into the upstream end of a rotary drum and serves to feed the waste foundry sand into the drum. The auger has a hollow shaft which carries a spiral flight and a blower is connected to the outer end of the shaft and acts to supply air through the shaft into the rotary drum.
In the construction of U.S. Pat. No. 4,941,822, the drum is heated externally by fuel burners and the excess air in the drum burns off the organic contaminants from the particulate material and calcines the mineral contaminants. Thus, the apparatus provides a complete removal of organic and inorganic contaminants from the foundry sand, so that the sand can be reclaimed for further use.
In practice, the apparatus of U.S. Pat. No. 4,941,822 operates at a drum temperature of about 1300.degree. F. The 1300.degree. F. temperature is required in order to have safe auto-ignition of any combustible fuel-air mixture generated within the drum by the process. While this elevated temperature is suitable for treating material, such as foundry sand, it has been found that certain contaminated particulate materials cannot be successfully treated at this temperature. For example, certain metals, such as brass, bronze and aluminum, cannot be heat treated at 1300.degree. F. because the metal surface will oxidize at this temperature and reduce the value of the treated metal. Moreover, contaminated soil containing hydrocarbons cannot by successfully treated at 1300.degree. F. because this temperature will calcine the hydrated mineral soil structure and the calcined soil will lose its ability to enhance plant growth, making the treated soil unsuitable for use.